The invention relates to an air spring or an air damper for the chassis of vehicles, the air spring comprising at least one working chamber filled with compressed air which is at least partially delimited by a rolling bellows, the rolling bellows rolling at least partially on rolling contours, being fastened at its ends by a frictional and/or positive connection to connecting parts and being partially provided at least one of its ends with a wall which is thicker in relation to the remainder of the rolling bellows body and/or with additional material layers.
Rolling bellows of air springs are subjected to high loads by clamping forces, not only at the clamping points but also in the regions where the rolling bellows have to absorb forces acting perpendicular to their axis, namely wheel guiding forces. Such forces cause a slight deflection of the bellows perpendicular to its axis and thus subject the “free” cross sections of the rolling bellows outside the clamping regions to load. This may become problematic in the case of thin-walled rolling bellows.
Thin-walled rolling bellows are, however, often desired in order to increase comfortable suspension characteristics and to reduce so-called harshness behavior. The person skilled in the art understands the term “harshness” as somewhat rough, hard suspension characteristics, superimposed in the event of vibrations of higher frequency and lower amplitude, which depend on the design, materials, intrinsic damping, inertia, etc. which are customary for air spring units and damper units.
With regard to the clamping forces which are critical for thin-walled rolling bellows, WO 2004/067989 A1 discloses an air spring comprising a rolling bellows in which both end regions are provided with short folded-up layers and/or are folded back or “turned up”. This folding-back takes place, however, only after the vulcanization of the rolling bellows. In a rolling bellows which is as thin-walled as possible and thus comfortably resilient, the reason for this folded-up portion is that the rolling bellows in the clamping region is intended to be thickened, i.e. doubled-up at the connecting parts, namely in the clamping region of the cover or the roll-off piston. This is necessary, in turn, with a thin-walled bellows, so as not to risk any material damage by pinching as a result of the clamping rings in the event of high clamping forces. In this air spring, the folded-up layer is attached to the bellows only after the vulcanization of the bellows and only in the clamping region. The remaining length of the rolling bellows is not reinforced.
In order to achieve the required strength even with thin wall thicknesses, rolling bellows are generally manufactured as fabric-reinforced, rubber bellows, a plurality of fabric or cord layers being able to be arranged superimposed over one another in the rubber matrix of the rolling bellows, the fibers thereof surrounding the rolling bellows at different angles. Often, layers with fibers which cross over one another (relative to the finished rolling bellows) are used.
A further possibility for achieving comfortable suspension characteristics and reduced “harshness” with thinner-walled rolling bellows, is to provide the rolling bellows and/or the air springs or air dampers with so-called external guides, namely with a tubular “supporting structure” or supporting body surrounding the rolling bellows. Thus, for example, a thin-walled rolling bellows may be surrounded by a thin-walled light metal tube as a supporting body.
The external guides may, in this case, be directly connected to the air spring cover so that the rolling bellows, on the one hand, may roll on the outside of the roll-off piston and, on the other hand, on the inner surface of the external guide. The difference remaining between the internal diameter of the external guide and the external diameter of the roll-off piston is thus relatively small for the rolled fold. Thus the problem arises that hardly any forces acting perpendicular to the axis of the rolling bellows are able to be absorbed, as even the slightest deflection of the bellows in the intermediate space (internal diameter of the external guide—external diameter of the roll-off piston) may already permanently damage the rolling bellows.
A solution for this technical problem is for the external guide not to be fastened to the air spring cover but at a slight distance therefrom on the rolling bellows as such. This is carried out, for example, by a clamping ring on the inner face of the rolling bellows, which clamps the external guide surrounding the rolling bellows at its upper end fixedly to the rolling bellows. The vertical distance between the air spring cover and the external guide i.e. the subsection of the rolling bellows in the vicinity of the cover not surrounded by the external guide, may now be used as a “joint”, which permits the pivotability of the air spring bellows in spite of the external guide and thus in turn allows the deflections produced by forces acting perpendicular to the axis of the rolling bellows. In the specialist field this subsection of the rolling bellows is referred to as the “cardanic fold” or “cardanic joint”.
Naturally this cardanic fold is subjected to high loads, so that for partial reinforcement of the rolling bellows during its production, additional material layers, namely fabric and/or rubber layers are already provided in the region of the cardanic fold produced subsequently to, and as a result of, the assembly of the air spring. The application of additional fabric and/or rubber layers is, however, only possible when manufacturing the rolling bellows individually and is also associated with a considerable additional manufacturing cost. Hitherto, with continuous manufacture from a rolling bellows “strand” there was only the possibility either of dispensing with a reinforcement of the cardanic fold or, alternatively, reinforcing the entire rolling bellows strand. The latter is undesirable, as already disclosed above, for reasons of comfort and “harshness”.
The object of the invention, therefore, is to provide an air spring or an air damper with a rolling bellows which is as thin-walled as possible, which may be made in a continuous production process, and which nevertheless has reinforcements or wall thickening in individual regions.